The present invention is directed generally to print heads for data terminals, and more particularly to a high speed dot matrix-type print head of improved construction wherein the actuator elements of individual print elements are arranged in a colinear configuration.
In recent years the increased use of data-based communication systems has led to the need for economical high speed data terminals whereby information conveyed by electrical signals is converted to printed copy on paper or other print-retaining medium. Typically, such teleprinters incorporate an impact type print head, which impacts the paper against a platen as the head moves across the paper, causing impressions to be made on the paper by an inked ribbon or by chemical transformation of the paper. The print head may be either of the type-bar type, wherein the impressions are formed by a selected one of a font of individual characters, or of the matrix-type, wherein selected ones of a plurality of individual print elements are forced against the paper to form the desired characters as the print head is stepped across the page. A preferred construction for a matrix-type teleprinter is shown in the copending application of Robert C. Hoffman, Richard H. Kruse, and Donald P. Martin, entitled "Teleprinter", Ser. No. 038,942, filed concurrently herewith and assigned to the present assignee.
One particularly successful form of matrix printer is the dot matrix printer, wherein the printing operation is performed by a plurality of elongated rod-shaped printing wires arranged in an array with ends thereof adjacent to the printing surface. To print a given character, selected ones of the printing wires are driven into contact with the paper to print a matrix of dots which collectively form the character. The character imprint may be accomplished in a single operation if a multi-column matrix of printing wires is provided, or in several steps if a single-column matrix of printing wires is provided. In either type of dot matrix printer, the printing wires are actuated at high speed many times in printing each line of material, either once per character or several times per character.
Each of the print wires in a dot matrix printer is connected to an actuator assembly, which ordinarily includes an electromagnet for forcing one end of the print wire against the paper, and a spring member for returning the print wire to a non-impacting position. To provide space for the actuator assemblies, which are ordinarily much larger in diameter than the print wires, print heads have been constructed with the actuator assemblies spaced apart, either arcuately in a horizontal plane, or arcuately in a vertical plane. From these spaced actuator assemblies, the print wires have either been directed to the printing surface in a straight line, and therefore have impacted the paper at an angle, as shown in U.S. Pat. No. 3,729,079, or have been guided by appropriate curved tubes or sheaths so as to impact the paper perpendicularly to the printing surface.
Where the print wires are directed in a straight line so as to contact the paper at an angle, a less-than-optimum impression is formed on the paper, and the print wire and actuator must be carefully adjusted to avoid objectionable deterioration of the printed character. Where the print wires are guided by a tube or sheath, friction between the wires and the sheath has tended to slow down the response time of the wires, making the print head unreliable in high speed applications. Furthermore, as a result of dirt, grease, moisture or other foreign matter collecting in the sheath, there has been a tendency for the print wires to stick, particularly when the teleprinter is operated in a sub-freezing or otherwise adverse environment, making the printer unreliable and adding to maintenance expense.
Another problem encountered in dot matrix-type print heads results from the extremely rapid actuation required of the print wires at high print rates, particularly in those print heads which utilize a single vertical column of print wires wherein individual print wires must be actuated several times to reproduce a single character. Where long printing wires are used, such as in the spaced-array type heads, the mechanical inertia of the long wires tends to limit maximum printing speed. For this reason, it is desirable that the print wire actuator assemblies be positioned as close to the printing surface as possible to minimize the length of the print wires.
A further disadvantage of spaced-apart print-wire actuator assemblies is that the print head requires a comparatively large volume, thereby complicating the design and construction of the carriage required to transport the print head across the paper.
One form of print head construction which obviates the above deficiencies is a colinear arrangement wherein the print elements are arranged side-by-side in close parallel-spaced relationship, with individual electromagnetic actuators thereof arranged coaxial to the print wires, one behind the other. Examples of such colinear print heads are shown in U.S. Pat. Nos. 3,963,108, 3,834,506 and 3,820,643. Unfortunately, such colinear print heads have heretofore been unnecessarily bulky and complex in construction, making them undesirably slow and expensive for use in teleprinters. The present invention provides a colinear-type print head of improved construction, wherein closely spaced print wires are provided in conjunction with individual actuator assemblies constructed of identical components adapted for mounting in a compact self-aligning frame assembly.
Accordingly, it is a general object of the present invention to provide a new and improved print head for use in a teleprinter or the like.
It is a more specific object of the present invention to form a new and improved print head which is simpler in construction and more reliable in operation.
It is another specific object of the present invention to provide a new and improved colinear-type print head wherein the print wire actuators are formed of identical components for improved manufacturing economy.